Prime movers, such as steam turbines, as well as other equipment, are generally protected from excessive speeds, by utilizing an emergency overspeed device to safely shut the unit down. Since such occurrences are very infrequent other devices are utilized to exercise the overspeed trip device to assure its operability at all times. Devices such as U.S. Pat. No. 3,508,443, Nutter are utilized to exercise the emergency gov. from standstill throughout the speed range. Still others use a fluid stream that is injected into the overspeed trip device, causing an unbalance, and hence a trip operation. The fluid stream method depends on rotational unbalance and cannot operate at very low speeds (U.S. Pat. 1,666,490, Dryer).
All of these devices have a common serious shortcoming, i.e., they lack the ability to produce a tripping action that serves as a calibration device. Therefore all emergency governors are tested for their set point only by operating the massive equipment throughout the speed range, until the set point is reached and the unit trips.
This invention permits disconnnecting the emergency trip device from the unit, protect the unit from accidental start-up by using protective interlocks, testing and calibrating the emergency trip device, without operating the massive prime mover and related equipment.